—IETF ForCES (Forwarding and Control Element Separation) is defining specifications for interfaces and modular resources abstractions in open programmable network equipments. According to drafts from ForCES, resources in the forwarding element are described in the form of Logical Function Blocks (LFBs), each of which has a single specific function of processing packets. In this paper, we first design the taxonomy of LFBs. Second, we design basic LFB classes and associated types. Designed LFBs have been submitted to IETF ForCES working group. Thirdly, we systematically analyze various aspects in the implementation of LFBs. Finally, our experiments show LFBs can be successfully operated.